Friday, November 28, 2014

Five hairstreaks of south Texas

Sweet face on a dusky blue groundstreak
Hairstreaks, of the subfamily Theclinae within the family Lycaenidae ("gossamer wings"), are small butterflies that are most diverse in the New World tropics [1]. I think they are highly underrated, as far as butterflies go. While they are certainly 'cute', telling them apart can be a challenge. Many of them are dainty gray butterflies with wing bands, eye-spots on their hindwings, and wispy tails.

I thought it might be instructive to go through key field markings. For this purpose, I searched through my back catalog and pulled images of five different species of hairstreak I've observed here in Texas. The subjects I've selected include three relatively similar-looking hairstreaks (the dusky blue groudstreak, the gray hairstreak, and the mallow scrub hairstreak) and two more distinctive hairstreaks (the great purple hairstreak and the silver banded hairstreak).

A gray hairstreak (Strymon melinus)
First, let's start with one of the most common and widespread hairstreaks in North America: the gray hairstreak. Larva tend to eat mallows and legumes, while adults are nectar generalists [2]. I would consider the gray hairstreak to be the "generic hairstreak", the hairstreak from which all others are differentiated. Note the relative cleanness and lack of clutter between the wing bands and wing edges. Also, remember the thickness, numbers, and placement of the orange markings on the hindwings. These are all traits that will vary from species to species.

Dusky blue groundstreak (Calycopis isobeon)
Now let's compare the gray hairstreak with the dusky blue groundstreak. This butterfly's larval food source matches its name ('groundstreak'): it's caterpillars feed on decaying leaf matter and other detritus [3]. At first glance these two hairstreaks look pretty similar. However, remember to check the eye-spots. The dusky has two well defined eye-spots outlined in red, versus the gray's one and a half. The dusky blue groundstreak has a third iridescent blue spot on the bottom edge of its hindwing, below the red and black eye-spots. This marking is totally missing in the gray hairstreak. The wing bands also differ- the dusky has obvious red outlining the post-medial band on its hindwings, and the thickness of this red outline is one of the field marks distinguishing it from its cousins. There's also provenance. The dusky blue groundstreak is only found in south Texas within the United States. If you anywhere but south Texas, then odds are it isn't a dusky blue groundstreak.

Mallow scrub hairstreak (Strymon istapa)
The mallow scrub hairstreak, which is actually in the same genus as the gray hairstreak, looks a bit different from the preceding two butterflies that I covered. When I saw this butterfly up in the canopy nectaring on Mexican olive (not pictured), I initially couldn't decide if it was a hairstreak or a tailed blue. I was better able to pick up on some of the identifying markers upon closer inspection.

Remember when I wrote about the uncluttered wings of the gray? The mallow scrub hairstreak is most definitely messy. There's a whole host of scribbles and bands in white and dark gray after the post-medial line. There's also minimal red on the eye-spots. Lastly, look at the front part of the hindwing and note the two dark gray spots. These two spots before the hindwing's band distinguish this hairstreak from all others. Like its con-generic the gray hairstreak, the mallow scrub hairstreak's caterpillars feed on mallows. This species is confined to the southern-most portions of the United States.

Another important thing to remember when identifying hairstreaks is that sometimes they don't have tails. The entire purpose of the eye-spotting and enticing tails on their hindwings is to encourage birds to take a nip there instead of other, more critical, areas. Many species of hairstreak even twitch and fidget their tails such that they resemble antennae.

Silver banded hairstreak (Chlorostrymon simaethis)
This silver banded hairstreak has seen better days. Either he's scrunched up, or something took a medium-sized chomp out of his right hindwing (he's scrunched up- ed.). The other side still seems to have its tail. Silver banded hairstreaks are another southern species. Their larvae are rather sly. Instead of feeding on leaves and exposing themselves to visual hunters, they hide inside the pods of balloon vines and eat the seeds [5]. This green hairstreak is pretty distinctive for a number of reasons. Its green coloration and straight silver bands are some of the easiest cues to pick up on in the field.

Great Purple Hairstreak (Altides halesus)
I'm going to end this post on the unmistakable great purple hairstreak. This butterfly has a wide distribution across southern North America. When I first saw this butterfly I was floored by its iridescent markings. The blue green markings on the edge of hindwings flashed in the sunlight whenever the butterfly re-arranged itself on the flower head. Its body is bright orange, and its wings are touched with bright blue. Their larvae eat mistletoe [6].

Obviously, this butterfly is quite distinct from most hairstreaks. However, the tells are still there. Like other hairstreaks, Great purples are petite with thin little tails, in contrast to the thick, chunkier tails on swallowtail butterflies. They also tend to sit with their wings folded, instead of spread to catch the sunlight.

In summary, many small butterflies with eye-spots and thread-like tails on their hindwings are in the Theclinae sub-family. After you have narrowed your search to this particular group, sorting through your options to get to species will probably require a combination of eye-spot characteristics,  wing band size and coloration, and location.  Good luck!

A silver-banded behind


1 comment:

  1. Nice post on hairstreaks. I really love their quiet beauty. I've got a lot of gray hairstreaks, but have only captured photos of 2 other hairstreaks: eastern tailed blue and juniper hairstreak, on our property. It seems like I ought to see more!